N-nitrosamine rejection by nanofiltration and reverse osmosis membranes: The importance of membrane characteristics

Abstract

The influence of membrane characteristics on the rejection of eight N-nitrosamines was investigated using one nanofiltration (NF), one seawater reverse osmosis (SWRO) and six low pressure reverse osmosis (LPRO) membranes. The rejection of the two lowest molecular weight N-nitrosamines, namely N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA), varied in the range from 8–82% to 23–94%, respectively. In general, the rejection of NDMA and NMEA increased with decreasing membrane permeability. The impact of membrane characteristics became less important for higher molecular weight N-nitrosamines. Among the four LPRO membranes (i.e. ESPA2, LFC3, TFC-HR and 70LW) that are commonly used for water reclamation applications, similar rejections were obtained for NDMA (37–52%) and NMEA (69–82%). In addition, rejection values of NDMA and NMEA among two LPRO membranes (i.e. ESPA2 and 70LW) were almost identical when compared under variable permeate flux and feed temperature conditions. However, it is noteworthy that the ESPAB membrane could achieve very high rejection of NDMA (as high as 71%) despite having a similar permeability to the LPRO membranes. Results reported here suggest that membrane characteristics associated with permeability such as the pore size and thickness of the active skin layer can be a key factor determining N-nitrosamine rejection.